i. FIELD OF THE INVENTION
The present invention relates to five-phase stepping motor systems ad particularly to methods and means for driving five phase stepping motors.
ii. DESCRIPTION OF THE PRIOR ART
Driving a stepping motor involves using a full step drive which effects angular movement over a predetermined angle, that is a step angle, in response to every pulse supplied to a drive circuit, and a half step drive which effects angular movement over half of the predetermined angle every pulse.
A drive circuit used in the full step drive of the five-phase stepping motor includes a drive circuit of a so-called pentagonal drive type including phase windings connected to each other to form a ring.
The drive circuit energizes phase windings connected in series with each other to form a ring, and includes pairs of transistors connected in series to each other with each pair having a connection connected to a corresponding junction between the phase windings. One transistor of each pair is connected to the positive pole of a d.c. power source and the other transistor of each pair is connected to the negative pole of the power source.
Prior drive circuits and phase windings of this type appear in FIGS. 4(a) and 4(b). Here the drive circuit performs a full step drive by turning on and off ten transistors T.sub.1, . . . ,
TABLE 1 ______________________________________ STEP 1 2 3 4 5 6 7 8 9 10 ______________________________________ T.sub.1 O O O O O T.sub.6 O O O O O T.sub.7 O O O O O T.sub.2 O O O O O T.sub.3 O O O O O T.sub.8 O O O O O T.sub.9 O O O O O T.sub.4 O O O O O T.sub.5 O O O O O .sup. T.sub.10 O O O O O ______________________________________
For example, in step 1, since transistors T.sub.1, T.sub.3, T.sub.5, T.sub.7, and T.sub.9 are turned on, currents shown by arrows of FIG. 4(a) flow through the phase windings. Further, in step 2, currents shown by arrows of FIG. 4(b) flow through four phase windings and effect a four-phase excitation.
In such a conventional drive, one of the pair of transistors for connecting the windings to the positive or negative pole of the power source is always on.
Accordingly, when the on and off state of the pair is reversed, a very large short-circuit current flows through a transistor pair from the positive pole of the power source to its negative pole due to delay of the off time of the transistor, and the pair of transistors generate heat. Thus, in order to prevent this problem, a delay circuit for the delaying turning on of the transistor has been required.